Induced fracture in hydrocarbon reservoirs, geothermal source rocks, and carbon storage sites is most commonly accomplished via hydraulic fracture techniques. These are profitable and widely employed in all three applications, but fall far short of optimal efficiency in extracting hydrocarbons, extracting heat, or injecting CO2, because (1) it is very difficult to achieve fracture spacing less than approximately 1 meter via this method, (2) a few fractures with high conductivity capture most of the fluid flow, 3) without reactive cracking, in situ mineral carbonation fills pore space and armors reactive surfaces thus reducing the overall amount of carbonation and/or requiring additional hydraulic fracturing, and (4) there are real and perceived risks of induced seismicity and groundwater contamination. Other reservoir stimulation techniques, via thermal cracking, acidification to produce “wormholes,” etc., have been considered but are not widely deployed.
Many unconventional reservoirs are characterized by low permeability and require hydraulic stimulation. However, the spacing of hydraulic fractures generally exceeds one meter. Such fracture networks extract less than, e.g., 1% pore fluid/year, for fluid pressure in fractures 10 MPa lower than rock, viscosity 0.001 Pa s, porosity 1%, and permeability 10-18 m2. Also, high water pressure—required to fracture tight gas and oil reservoirs—can induce earthquakes. Hydraulic stimulation generally fails to produce sufficient connectivity between injection and production wells, transports fluid away from production wells, or creates a few large fractures around which thermal energy is rapidly extracted and exhausted.